The design of certain types of vehicle body styles necessitates the storage of the spare tire under the vehicle. This mode of spare tire storage is of particular advantage with pick-up trucks, mini-vans and other vehicles. In such applications, a winch is mounted on the underside of the vehicle carriage for winding or unwinding a cable having the spare tire carried on an end fitting thereof. The winch is used to wind the cable on a spool to draw the spare tire against the underside of the vehicle carriage and unwind the cable from the spool to lower the spare tire to the ground for access and use. U.S. Pat. Nos. 4,059,197; 4,535,973; 4,544,136 and 4,625,947 describe tire lift/carrier winches for such applications.
An overload clutch mechanism has been used in such tire lift/carrier winches to allow winch operation only when the load on the spool is within a maximum prescribed limit. For example, in the event the operator of the winch attempts to actuate the winch when the cable spool is subjected to an overload (e.g. such as when the spare tire is fully lifted or its upward movement is obstructed), the clutch mechanism functions to disengage the cable winding spool and the manually actuated drive shaft of the winch to prevent damage to the winch components.
Various types of spring clutch mechanisms have been developed to this end. U.S. Pat. Nos. 4,544,136 and 4,625,947 illustrate spring clutch mechanisms employed between the drive shaft and the cable winding spool of the winch wherein a plurality of springs are caused to deflect out of driving relation with an adjacent clutch component in an overload situation to prevent rotation of the cable winding spool by the drive shaft.
In a particular tire lift/carrier winch sold commercially by a subsidiary of Applicant's assignee, the spring clutch comprises three springs manufactured to precise tolerances to interlock and function as a single ring that in an overload situation is deflected out of generally circular shape. In this spring clutch, the springs are arranged in an annular array on a clutch driven plate with opposite ends of the springs interlocked. In the normal drive mode (static mode), an intermediate portion of each spring rests against a retaining tab formed on the driven plate. In an overload situation, the interlocked opposite ends of adjacent springs are displaced (deflected) radially outward by the drive plate and the intermediate portion of each spring moves radially inward away from the respective retaining tab as the ring is deflected out of circular shape. The reaction direction of each spring to such deflection is generally parallel with the respective retaining tab.
It is an object of the invention to provide a clutch mechanism for a winch, such as a tire lift/carrier winch, having significantly reduced tolerance requirements for the clutch springs.
It is another object of the invention to provide such a clutch mechanism wherein the clutch provides more consistent and precise tripping torques (i.e. the torque needed to disengage the clutch from the driving mode).
It is another object of the invention to provide such a clutch mechanism exhibiting minimal decay of the tripping torque after anticipated cycles of use.
It is another object of the invention to provide such a clutch mechanism producing significantly reduced variations in cable tension during operation of the clutch.